In automated clutch applications, such as dual clutch or multiple clutch applications, for example, a precise knowledge of the clutch torque is particularly important for the gearshift and driveaway characteristics of the vehicle.
In a hybrid vehicle having a hybrid drivetrain the traction resistance from two independent energy sources, such as the fuel of an internal combustion engine and electrical energy from a traction battery of an electric motor, can be overcome by conversion into mechanical energy. WO 2008/064633 A1 discloses a method and a device for the adaptation of a hybrid disconnect clutch in a vehicle hybrid drive, which is arranged between the internal combustion engine and an electric motor. In the method, the internal combustion engine is shut down and once the internal combustion engine has been switched off, the hybrid disconnect clutch is opened. Then, with the internal combustion switched off and the hybrid disconnect clutch opened, a time gradient of the speed of the internal combustion engine is registered. After partial closing of the hybrid disconnect clutch, as soon as the speed of the internal combustion engine has fallen below a predefined value, the time gradient of the speed of the internal combustion engine is determined with the clutch partially closed. The characteristic curve of the hybrid disconnect clutch is then adapted on the basis of the determined clutch torque transmitted by the partially closed hybrid disconnect clutch. Here the characteristic curve is parameterized by two characteristic variables such as the touch point and the clutch co-efficient of friction. The touch point shifts the clutch characteristic curve as a function of the travel, whilst the co-efficient of friction scales the torque value of the clutch characteristic curve.
In order to be able to adapt the co-efficient of friction reliably, the disconnect clutch must be set to a slipping state with a high clutch torque, a sufficiently frequent good torque quality of the internal combustion engine being necessary. If the hybrid disconnect clutch is used mainly in just two operating modes, closed or opened, however, situations in which slip can occur for adaptation of the co-efficient of friction are rare. Moreover, in situations where the internal combustion engine is started using the hybrid disconnect clutch the internal combustion engine torque is imprecise.
In addition, the overall system has a tendency for oscillations, which leads to an increased detection of apparent slipping states, although the disconnect clutch is fully closed and the internal combustion engine is delivering little torque. Such apparent slipping states lead to a deficient reduction of the co-efficient of friction and therefore drastically reduce the torque accuracy of the system. A slip control allows precise adjustment of the selected slip on the disconnect clutch, but such a slip control is very expensive.
Ramping up the co-efficient of friction until slipping occurs is also known. Such a ramping up of the co-efficient of friction, however, leads again and again to slipping in all driving situations, regardless of which mode the disconnect clutch is in.